From the very beginning, Naruto is a series that places great importance on bloodlines, lineage, clans, family, and country. The series constantly is looking backwards to previous 3-man teams, Hokages, and eras to contrast the present. As naturally as the series engages in the connection between Naruto and his teacher ( who was taught by his father, who is taught by his current mentor, who was taught by the current sitting Hokage) it also engages in Sasuke and his lineage back through history. Creating a character who lived long ago that is the intersection of their two lineages isn't crazy. Nor is the fact that if the two greatest clans powers existed in one person, that guy would be crazy strong.